Navigating Rotary Bored Piling: Answering Your Top Questions

Rotary bored piling and Continuous Flight Auger (CFA) piling are both widely used techniques for creating deep foundations, but they differ significantly in their methodology. Both methods involve drilling into the ground to create piles, as opposed to a displacement pile such as driven precast concrete piling. Rotary bored piling uses an auger or drilling bucket to excavate soil, which is then removed from the borehole using a temporary casing or by flushing it out with a drilling fluid. CFA piling uses a continuous helical auger that remains within the borehole, with concrete pumped through the hollow stem as the auger is withdrawn.

The concrete pouring is the key difference. With rotary bored piling the concrete is poured into a prepared borehole which is held open. In CFA piling, the drilling and concrete pouring is a simultaneous operation with the concrete pumped down the auger’s flight as it is extracted from the borehole.

Rotary bored piling is a highly flexible method of piling with many adaptations available for ground conditions and any specific project requirements. The ability to use either temporary casing or a drilling fluid means that ground conditions can be accounted for and a variety of ancillary drilling equipment can be deployed if needed. This flexibility means that a custom installation methodology can be utilised for each site, ensuring optimal outcomes in diverse geological settings.

Rotary bored piling is not without its drawbacks. Whilst its versatility and adaptability mean that it is suitable for almost any piling site, this comes with an associated cost. Equipment and expertise needed can result in higher initial costs when compared with alternative methodology like CFA piling and therefore can make it a less economical option.

The other economic disadvantage is it is a slower process than CFA or driven alternatives. Due to the technical nature of the work, the piles take longer to install and therefore, projects can have longer programmes.

Another notable disadvantage is the potential for groundwater contamination during drilling operations, especially in permeable ground conditions where drilling fluid may seep into surrounding aquifers. This can be handled by close observation and skilled workforce, or by using temporary casing.

Finally, the technique may encounter limitations in restricted access sites or areas with overhead obstructions, necessitating careful planning and coordination to overcome logistical challenges.